core: remove libsystemd dependency (#5660)

* remove libsystemd dependency

as per Lennart Poettering's advice:
https://github.com/systemd/systemd/issues/32028#issuecomment-2031366922

* fix naming for systemd helper functions

* rename vars according to code style

* Nix: update meson patch

---------

Co-authored-by: Mihai Fufezan <[email protected]>

7 files changed, 76 insertions, 31 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index b5e45d7b..8c206b7a 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -192,20 +192,8 @@ endif()
 if(NO_SYSTEMD)
     message(STATUS "SYSTEMD support is disabled...")
 else()
-    message(STATUS "SYSTEMD support is requested (NO_SYSTEMD not defined) checking deps...")
-    check_include_file("systemd/sd-daemon.h" SYSTEMDH)
-    if(SYSTEMDH)
-        pkg_check_modules(LIBSYSTEMD libsystemd)
-        if (LIBSYSTEMD_FOUND)
-            add_compile_definitions(USES_SYSTEMD)
-            target_link_libraries(Hyprland "${LIBSYSTEMD_LIBRARIES}")
-            message(STATUS "Systemd found")
-        else()
-            message(WARNING "Systemd support requested but systemd libraries were not found")
-        endif()
-    else()
-        message(WARNING "Systemd support requested but systemd headers were not found")
-    endif()
+    message(STATUS "SYSTEMD support is requested (NO_SYSTEMD not defined)...")
+    add_compile_definitions(USES_SYSTEMD)
 endif()
 
 set(CPACK_PROJECT_NAME ${PROJECT_NAME})
diff --git a/meson.build b/meson.build
index dd73cb92..40883073 100644
--- a/meson.build
+++ b/meson.build
@@ -52,14 +52,9 @@ endif
 
 backtrace_dep = cpp_compiler.find_library('execinfo', required: false)
 epoll_dep = dependency('epoll-shim', required: false) # timerfd on BSDs
-systemd_dep = dependency('libsystemd', required: get_option('systemd'))
 
 if get_option('systemd').enabled()
-  if systemd_dep.found()
-    add_project_arguments('-DUSES_SYSTEMD', language: 'cpp')
-  else
-  	error('Cannot enable systemd in Hyprland: libsystemd was not found')
-  endif
+  add_project_arguments('-DUSES_SYSTEMD', language: 'cpp')
 endif
 
 if get_option('legacy_renderer').enabled()
diff --git a/nix/patches/meson-build.patch b/nix/patches/meson-build.patch
index 5827e5c3..eb1d3f9a 100644
--- a/nix/patches/meson-build.patch
+++ b/nix/patches/meson-build.patch
@@ -1,5 +1,5 @@
 diff --git a/meson.build b/meson.build
-index 1d2c7f9f..c5ef4e67 100644
+index 40883073..d8f2e536 100644
 --- a/meson.build
 +++ b/meson.build
 @@ -33,20 +33,7 @@ if cpp_compiler.check_header('execinfo.h')
@@ -24,7 +24,7 @@ index 1d2c7f9f..c5ef4e67 100644
    add_project_arguments('-DNO_XWAYLAND', language: 'cpp')
  endif
  
-@@ -69,8 +56,6 @@ if get_option('buildtype') == 'debug'
+@@ -65,8 +52,6 @@ if get_option('buildtype') == 'debug'
    add_project_arguments('-DHYPRLAND_DEBUG', language: 'cpp')
  endif
  
@@ -34,7 +34,7 @@ index 1d2c7f9f..c5ef4e67 100644
  headers = globber.stdout().strip().split('\n')
  foreach file : headers
 diff --git a/src/meson.build b/src/meson.build
-index 45701f5f..3505cefe 100644
+index 15c69552..327aa4fb 100644
 --- a/src/meson.build
 +++ b/src/meson.build
 @@ -9,7 +9,7 @@ executable('Hyprland', src,
@@ -46,7 +46,7 @@ index 45701f5f..3505cefe 100644
      dependency('cairo'),
      dependency('hyprcursor'),
      dependency('hyprlang', version: '>= 0.3.2'),
-@@ -17,11 +17,11 @@ executable('Hyprland', src,
+@@ -17,10 +17,10 @@ executable('Hyprland', src,
      dependency('egl'),
      dependency('xkbcommon'),
      dependency('libinput'),
@@ -54,7 +54,6 @@ index 45701f5f..3505cefe 100644
 +    dependency('xcb', required: get_option('xwayland')),
      backtrace_dep,
      epoll_dep,
-     systemd_dep,
 -    udis86,
 +    dependency('udis86'),
  
diff --git a/src/Compositor.cpp b/src/Compositor.cpp
index bc229d32..edf7c25d 100644
--- a/src/Compositor.cpp
+++ b/src/Compositor.cpp
@@ -8,7 +8,7 @@
 #include "debug/HyprCtl.hpp"
 #include "debug/CrashReporter.hpp"
 #ifdef USES_SYSTEMD
-#include <systemd/sd-daemon.h> // for sd_notify
+#include <helpers/SdDaemon.hpp> // for SdNotify
 #endif
 #include <ranges>
 #include "helpers/VarList.hpp"
@@ -385,8 +385,8 @@ void CCompositor::cleanup() {
     Debug::shuttingDown = true;
 
 #ifdef USES_SYSTEMD
-    if (sd_booted() > 0 && !envEnabled("HYPRLAND_NO_SD_NOTIFY"))
-        sd_notify(0, "STOPPING=1");
+    if (Systemd::SdBooted() > 0 && !envEnabled("HYPRLAND_NO_SD_NOTIFY"))
+        Systemd::SdNotify(0, "STOPPING=1");
 #endif
 
     // unload all remaining plugins while the compositor is
@@ -615,10 +615,10 @@ void CCompositor::startCompositor() {
     g_pHyprRenderer->setCursorFromName("left_ptr");
 
 #ifdef USES_SYSTEMD
-    if (sd_booted() > 0) {
+    if (Systemd::SdBooted() > 0) {
         // tell systemd that we are ready so it can start other bond, following, related units
         if (!envEnabled("HYPRLAND_NO_SD_NOTIFY"))
-            sd_notify(0, "READY=1");
+            Systemd::SdNotify(0, "READY=1");
     } else
         Debug::log(LOG, "systemd integration is baked in but system itself is not booted à la systemd!");
 #endif
diff --git a/src/helpers/SdDaemon.cpp b/src/helpers/SdDaemon.cpp
new file mode 100644
index 00000000..0835637a
--- /dev/null
+++ b/src/helpers/SdDaemon.cpp
@@ -0,0 +1,58 @@
+#include "SdDaemon.hpp"
+
+#include <memory>
+
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+namespace Systemd {
+    int SdBooted(void) {
+        if (!faccessat(AT_FDCWD, "/run/systemd/system/", F_OK, AT_SYMLINK_NOFOLLOW))
+            return true;
+
+        if (errno == ENOENT)
+            return false;
+
+        return -errno;
+    }
+
+    int SdNotify(int unsetEnvironment, const char* state) {
+        int fd = socket(AF_UNIX, SOCK_DGRAM, 0);
+        if (fd == -1)
+            return -errno;
+
+        constexpr char envVar[] = "NOTIFY_SOCKET";
+
+        auto           cleanup = [unsetEnvironment, envVar](int* fd) {
+            if (unsetEnvironment)
+                unsetenv(envVar);
+            close(*fd);
+        };
+        std::unique_ptr<int, decltype(cleanup)> fdCleaup(&fd, cleanup);
+
+        const char*                             addr = getenv(envVar);
+        if (!addr)
+            return 0;
+
+        // address length must be at most this; see man 7 unix
+        size_t             addrLen = strnlen(addr, 107);
+
+        struct sockaddr_un unixAddr;
+        unixAddr.sun_family = AF_UNIX;
+        strncpy(unixAddr.sun_path, addr, addrLen);
+        if (unixAddr.sun_path[0] == '@')
+            unixAddr.sun_path[0] = '\0';
+
+        if (!connect(fd, (const sockaddr*)&unixAddr, sizeof(struct sockaddr_un)))
+            return 1;
+
+        // arbitrary value which seems to be enough for s-d messages
+        size_t stateLen = strnlen(state, 128);
+        if (write(fd, state, stateLen) >= 0)
+            return 1;
+
+        return -errno;
+    }
+}
diff --git a/src/helpers/SdDaemon.hpp b/src/helpers/SdDaemon.hpp
new file mode 100644
index 00000000..7b2b5de1
--- /dev/null
+++ b/src/helpers/SdDaemon.hpp
@@ -0,0 +1,6 @@
+#pragma once
+
+namespace Systemd {
+    int SdBooted(void);
+    int SdNotify(int unset_environment, const char* state);
+}
diff --git a/src/meson.build b/src/meson.build
index d490cddb..15c69552 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -20,7 +20,6 @@ executable('Hyprland', src,
     xcb_dep,
     backtrace_dep,
     epoll_dep,
-    systemd_dep,
     udis86,
 
     dependency('pixman-1'),